The fundamental challenge faced by all photodetectors in the mid/far-infrared spectral region stems from the need to use a low-energy transition for the photo-absorption in narrow bandgap semiconductors, quantum nanostructures, or low-energy impurity transitions. This inevitably results in high dark current due to thermal excitations, which limits the overall performance of the detector. Dark current is alleviated at low temperatures where commercial and conventional, single-element photocurrent and photovoltaic detectors can provide excellent performance, with detectivities, D*, of about 1011 cm.Hz1/2 W−1 for liquid nitrogen cooled detectors. However, the cryogenic cooling requirement limits applications of such systems. Thermoelectric-cooled and room temperature detector elements have much lower detectivities D* of about 109 cm.Hz1/2 W−1 and 107 cm.Hz1/2 W−1, respectively.
Therefore, a need remains for an infrared photodetector that can operate near room temperature with low dark current.